It is conventional for aircraft to include as standard equipment backup power supplied for use in times of power outage in the form of air driven turbines which are lowered into the airstream. The turbines make use of the relative speed of the aircraft through the ambient air to cause the turbine blades to rotate. The rotation imparted to the blades due to their movement through the air is then used to drive electrical generating gear or provide hydraulic power to the aircraft hydraulic system during the aforementioned times of power outages. These arrangements conventionally include governor mechanisms that control the output rotational speed delivered from the blades to electrical or hydraulic units that are designed to operate most efficiently at a set or given speed.
An example of such a control system is shown in U.S. Pat. No. 4,411,596 to Chilman, dated Oct. 25, 1983 and assigned to the assignee of this invention. Chilman discloses a blade pitch control mechanism for a turbine blade mounted for rotation in a hub assembly. The control mechanism includes a drive member mounted for reciprocation along a central axis of the hub assembly. The drive member has a control member secured to one end and a seat member at the other end. The blade has operatively coupled thereto, a centrifugally responsive means which includes a pin in mating engagement with the control member. A spring is positioned between the hub assembly and the control member to thereby cause the blade to assume a course or high pitch position when the blade and hub assembly are in storage. A slide member is mounted on a portion of the hub assembly for reciprocation along the central axis. A spring is positioned between the seat member and the slide member. A flyweight is supported on the hub assembly and engages the slide member. Rotation of the hub assembly causes the flyweight to move the slide member and thereby move the blade pitch from course pitch to fine pitch and, thereafter, allow the centrifugally responsive means to control the blade pitch.
Although the Chilman control system is quite effective, there is a need for a simplified ram air turbine control which is of lighter weight, lower in cost and comprising a smaller envelop. This invention is directed to solving this need and provides a ram air turbine control system of the character described which completely eliminates the centrifugally responsive means coupled to the turbine blade.